Printing apparatus of the type with which the present invention is concerned include thermal printers of the type disclosed in EP-A-322918 and EP-A-322919 (Brother Kogyo Kabushiki Kaisha) and EP-A-0267890 (Varitronics). These printers each include a printing device having a cassette receiving bay for receiving a cassette or tape holding case. In EP-A-0267890, the tape holding case houses an ink ribbon and a substrate tape, the latter comprising an upper image receiving layer secured to a backing layer by adhesive. In EP-A-322918 and EP-A-322919, the tape holding case houses an ink ribbon, a transparent image receiving tape and a double-sided adhesive tape which is secured at one of its adhesive-coated sides to the image tape after printing and which has a backing layer peelable from its other adhesive-coated side. With both these apparatus, the image transfer medium (ink ribbon) and image receiving tape (substrate) are in the same cassette.
The present applicants have developed a different type of printing apparatus which is described for example in copending British Application No. 9212423.9, the contents of which are herein incorporated by reference.
In this printing apparatus, the substrate tape is similar to that described in EP-A-0267890 but is housed in its own tape holding case while the ink ribbon is similarly housed in its own tape holding case.
In all of these cases, the image receiving tape passes in overlap with the ink ribbon through a print zone consisting of a print head and a platen against which the print head can be pressed to cause an image to transfer from the ink ribbon to the image receiving tape. There are many ways of doing this, including dry lettering or dry film impression, but the most usual way at present is by thermal printing where the print head is heated and the heat causes ink from the ink ribbon to be transferred to the image receiving tape. With the printing apparatus described in GB 9212423.9, the tape holding case with the ink ribbon is placed on one side of the print zone while the tape holding case with the substrate is placed on the other side of the print zone. In these printing apparatus, the tape holding case is commonly referred to as a cassette.
The printing apparatus of GB 9212423.9 and of EP 322919 have a lid or cover member which covers a cassette receiving bay arranged to receive the cassette. It is one object of the present invention to inhibit operation of the printer unless the lid or cover member is in its correct position.
If an attempt is made to operate the thermal printing apparatus without a cassette inserted therein, a situation can arise where the print head contacts the platen directly, without the interposition of tape and/or ink ribbon. In this case, heat at the thermal print head could cause melting or damage to the platen and leave deposits on the print head. It is also thus desirable to determine when a tape holding case is in place and to allow operation of the printing apparatus only in these circumstances. Where only one cassette is required, detection of the presence of this cassette is desirable. Where two cassettes are required, it is desirable to ascertain that at least one cassette is present.